Technical Field
The present invention relates to a kind of pixel driving circuit and its driving method. More particularly, the present invention relates to a pixel driving circuit and its driving method less affected by high-frequency effects.
Description of Related Art
Televisions and tablet computers with liquid crystal display (LCD) are popular recently, and technology of LCD develops rapidly. In general, the liquid crystal display is able to show different grayscales by providing data signals to control the degree of deflection of liquid crystal (LC) molecules.
However, to let LCDs have higher resolutions and higher refresh rate, the LCDs require scan signals and data signals with higher operating frequency. The operating frequency influences a dielectric coefficient of liquid crystal molecules. When the operating frequency is higher, the dielectric coefficient will be lower. When the dielectric coefficient is reduced, a capacitance of the LC decreases, such that a stored charge between two terminals of the LC capacitor will drop. The reduced voltage difference between two terminals of the LC capacitor caused by inadequate charge further influences a deflection of LC molecules and a grayscale display function of the LCD.
One of known solutions is implementing additional storage capacitors to stabilize aforesaid dropping of the voltage difference. However, it requires a large area to implement these storage capacitors, so as to cause a severe loss of aperture ratio of the display device, especially for applications with a high operating frequency (e.g., field sequential display) or applications with a high dielectric coefficient (e.g., blue phase liquid crystal or ferroelectric liquid crystal).
Besides, sub-threshold currents of driving transistors in the pixel circuit induce over-charge voltages to the LC capacitors and also lead to excessive power consumption. Also, a threshold voltage of the driving transistor under a long-term current stress will lead to a deviation problem.